The present invention relates to cartons, and more particularly to cartons of the tray and lid type which are fabricated from paperboard for packaging food. The tray type cartons disclosed herein are especially useful as ovenware for both conventional and microwave ovens.
Tray type cartons are old in the art. In the past such cartons have been fabricated from both paperboard and metal. Such cartons must be leakproof so that they are capable of handling liquid and semi-liquid foods. However, with the advent of microwave ovens, paperboard cartons have been growing in popularity because of their broader utility. Paperboard, when properly treated with heat resistant coatings, is equally useful as a carton material for both conventional and microwave ovens, whereas metal cannot be used in a microwave oven.
One such tray structure is disclosed in U.S. Pat. No. 4,351,473 granted to Guelfo A. Manizza. The tray and cover structure disclosed in Manizza is designed with a removable lid portion which leaves a portion of the cover attached to the flange area of the tray when the lid is removed. However, the structure of Manizza still suffers from a lack of structural rigidity after the lid is removed, especially when liquid or semi-liquid products are packaged. In Manizza, the portion of the cover which remains attached to the flange is no greater than, and actually slightly less than the width of the flange area when the lid is removed. Thus it is difficult and sometimes impossible to pick up the tray of Manizza by grasping one corner after the lid has been removed.
In accordance with the present invention, a tray structure substantially as shown in Manizza has been made substantially stronger simply by moving the cut lines in the cover member which form the lid cut out inwardly away from the tray flange area. In doing so, the opening in the cover provided by the removable lid is reduced, but the remaining cover material left intact around the periphery of the flange increases the strength of the tray by a surprizing amount as compared with the strength of a non-reinforced structure, or a structure which is partially reinforced as taught by Manizza.